Tipping-off method



Oct. 18, 1960 w. R. MADIGAN TIPPING-OFF METHOD Filed May 14, 1957INVENTOR. WILLIAM F5. MADIGAN FUTORNEY.

United States Patent 'ice TIPPlNG-OFF METHOD William R. Madigan,Fairmont, W. Van, assignor to Westinghouse Electric Corporation, EastPittsburgh, Pa, a corporation of Pennsylvania Filed May 14, 1957, Ser.No. 659,130

6 Claims. (CI. 4978) The present invention relates to a method ofsealing evacuated discharge and incandescent lamps and, moreparticularly, to a method of tipping-oil? the exhaust tubulation of saidexhausted lamps.

In the tipping-ofi of evacuated discharge lamps, such as for examplefluorescent lamps, it is extremely desirable to form the tip-off on theexhaust tubulation as close to the lamp seal as possible to protect thetip-ofi from contact with the base which is applied about the seal andtip-oil dtuing the later basing operation.

Heretofore, the exhaust tubulation of evacuated discharge lamps, such asfor example fluorescent lamps, have been tipped-oft by the methoddisclosed in U.S. Patent No. 2,561,838, issued July 24, 1951, to C. E.Bechard, which method comprises difierentially heating opposite sides ofthe exhaust tubulation to 01m a bubble within the tubulation therebyclosing off the tubulation. The formation of the bubble is accomplishedby heating a larger area of one side of the tubulation with greaterintensity than the opposite side thereof. This method of differentialheating of the exhaust tubulation by burners limits the proximity of thetipofl3 to the lamp seal. If the tip-off is desirably achieved close tothe lamp seal, the burner fires often undesirably heat and resultantlystrain the seal which strain may subsequently result in a cracked sealthus producing a defective lamp. Further, due to drafts around theexhaust head it is extremely difficult to control the fire splashpattern on the opposite sides of the exhaust tubulation, to form thebubble at a desired point. While an increase in the pressure of thegas-air mixture in the burners will pin-point the fire pattern on thetubulation at the desired point, it may result in a change in thetemperature of the fires or result in back firing, i.e. an explosionwithin the gas line which ruptures the line. In addition, if the bubbleforming fire is too sharp a thin bubble is formed within the tubulationand the tire follows the retreating wall of the bubble with resultantfurther heating and further undesirable thinning of the wall therein.

It is the general object of the present invention to avoid the foregoingand other ditficulties of and objections to the prior art practices bythe provision of a method of formin a bubble-type tip-off in the exhausttubulation of an evacuated device, such as a discharge or incandescentlamp, which method provides positive control over the location of thebubble formed in the exhaust tubulation and permits its formation closeto the lamp seal without dmaging the seal.

A specific object of the present invention is the provision of a methodof tipping-off an exhaust tubulation of an evacuated discharge lampwhich method prevents any undesirable thinning of the wall of the bubbleduring formation thereof.

The aforesaid objects of the invention, and other objects which willbecome apparent as the description proceeds are achieved by providing amethod of tippingoff the exhaust tubulation of an evacuated device whichmethod comprises heating a Zone of the exhaust tubula- Patented Oct. 18,1960 tion to a plastic condition to cause the sides of the tubulation tosuck in and directing a jet of predetermined pressure and directionagainst a predetermined point in the heated zone to form a bubble andsimultaneously cool the wall of the forming bubble to prevent furtherthinning thereof.

Referring to the accompanying drawing in which like numerals ofreference indicate similar parts throughout the several views:

Fig. 1 is a side elevational view of a portion of an exhaust head inwhich a discharge device such as a fluorescent lamp is secured by itsexhaust tubulation and showing a heat bafile for protecting the seal andlead wires, the burners and the air nozzle positioned about thetubulation.

Fig. 2 is an enlarged plan view along the line IIII of Fig. 1 in thedirection of the arrows.

Fig. 3 is an enlarged vertical sectional view of a portion of theexhaust tubulation illustrating the preliminary phase of the tip-oftmethod wherein the walls of the tubulation above the bubble arecommencing to collapse and the bubble is beginning to form.

Fig. 4 is a vertical sectional view along the line IV-IV of Fig. 3 inthe direction of the arrows.

Fig. 5 is a horizontal sectional view along the line V-V of Fig. 3 inthe direction of the arrows.

Fig. 6 is a view similar to Fig. 3 but showing an intermediate step inthe forming of the bubble in the converging wall of the tubulation.

Figs. 7 and 8 are side elevational views of the finished tip-oft andshowing the spherical dome of the bubble.

Although the principles of the invention are broadly applicable to amethod for tipping-0E an evacuated device, such as a discharge orincandescent lamp, the invention is particularly adapted to thetipping-off of fluorescent lamps and hence it has been illustrated andwill be so described.

With specific reference to the form of the invention illustrated in thedrawings there is shown in Fig. 1, an electric lamp 10, such as afluorescent lamp, secured by means of its exhaust tubulation 12 in anexhaust head 14 of the type shown in U.S. Patent No. 2,254,905, issuedSeptember 2, 1941, to D. Mullan, which head 14 may be part of an exhaustmachine of the type shown in U.S. Patent No. 2,247,513, issued July 1,1941, to A. J. Marshaus. As is well known in the art, the exhausttubulation 12 connects the interior of the lamp 10 with the exhaust head14 to permit the evacuation and exhaust of the lamp 1!). In order toprotect a seal 16 and lead wires 18 of the lamp 1% during thetipping-off operation, a conically shaped heat bafile 2d of the typeshown in the above mentioned U.S. Patent No. 2,247,513 is shown in theoperating position.

For the purpose of uniformly plasticizing a zone A (Fig. 3) of theexhaust tubulation 12 in the desired location where the bubble is to beformed, a pair of identical tipping-ofi burners 2-2 are disposed in thesame horizontal plane on opposite sides of the exhaust tubulation 12. Toprovide a bubble forming control means for use, as hereinafter related,an air nozzle 24 is disposed for convenience at right angles to theburners 22 and in the same horizontal plane as the burners 22. The airnozzle 24 continuously directs a circular jet of compressed air at roomtemperature, under a pressure of about 7 lbs. per square inch, which airjet has a diameter comparable to the desired diameter of the opening ofa bubble 26, at a predetermined area B in the zone A.

In accordance with the present invention after the lamp 10 has beenevacuated in the usual manner through the exhaust tubulation 12 andfilled with a predetermined amount of mercury and an inert gas, such asargon, the zone A of the exhaust tubulation 12 is uniformly heated bythe burners 22 to the plastic condition to enable the atmosphericpressure to cause a uniform collapse inwardly of the wall of thetubulation, as shown in Figs. 3, 4 and 5. During this inward collapse.of the wall from the position shown in Figs. 1 and 2 to the positionshown in Figs. 3, 4 and 5, the jet of compressed air from the nozzle 24directed at the area B begins to drive the wall of the exhausttubulation thereat inwardly to join the glass at the opposite side walland such air jet simultaneously cools the wall on the forming bubble 26to prevent undue thinning or weakening thereof. Simultaneously, with theformation of the bubble 26 the lamp is pulled downwardly by a mechanism(not shown) which carries the heat baffie 25) to stretch and thin thecollapsing wall at point C of Fig. 6. Continued heating of the zone A bythe burners 22. moves the collapsing side wall of the exhaust tubulation12 thereat from the position shown in Fig. 6 to the position shown inFig. 7 to sever the tubulation 12 and produce the resultant sphericallyshaped tip shown in Figs. 7 and 8, which tip is desirably about 1 mm.shorter than the tip shown in the above mentioned US. Patent No'2,561,838.

. It will thus be obvious to those skilled in the art that a method oftipping-off an exhaust tubulation of an evacuated lamp has been providedwhich achieves positive control over the location of the bubble which isformed in the exhaust tubulation and permits the formation of the bubbleclose to the lamp seal without damaging the latter. In addition, thetip-oi method of the present invention prevents any undue thinning orweakening of the wall of the bubble during the formation thereof.

While in accordance with the patent statutes, one bestknown embodimentof the invention has been illustrated and described in detail, it is tobe particularly understood that the invention is not limited thereto orthereby.

I claim:

1. The method of tipping-off a vitreous exhaust tubulation protrudingfrom an evacuated device which comprises uniformly heating a zone of theexhaust tubulation to cause the wall thereof to collapse inwardly,directing a jet of a fluid at a predetermined area in said heated zoneto cause said area to be driven into said tubulation to join with theopposite wall thereof and to form a bubble thereby closing off thetubulation and cooling it to prevent undue thinning of the wall of saidbubble, and continuing the heating of said zone to sever the collapsingwall of said tubulation and to form a dome for said bubble.

2. The method of tipping-01f a vitreous exhaust tubulation protrudingfrom an evacuated device having a seal which comprises shielding theseal of said device from heat, uniformly heating a zone of the exhausttubulation to cause the wall thereof to collapse inwardly, directing ajet of a fluid at a predetermined area in said heated zone to cause saidarea to be driven into said tubulation to join with the opposite wallthereof and to form a bubble thereby closing off the tubulation andcooling it to prevent undue thinning of the wall of said bubble, andcontinuing the heating of said zone to sever the collapsing Wall of saidtubulation and to form a dome for said bubble.

3. The method of tipping-01f a vitreous exhaust tubulation protrudingfrom an evacuated lamp having a seal which comprises shielding the sealof said lamp from heat, uniformly heating a zone of the exhausttubulation to cause the wall thereof to collapse inwardly, directing ajet of a fluid at a predetermined area in said heated zone to cause saidarea to be driven into said tubulation to join with the opposite wallthereof and to form a bubble thereby closing off the tubulation andcooling it to prevent undue thinning of the wall of said bubble andsimultaneously stretching the collapsing zone of said tubulationlongitudinally to thin the wall thereof While continuing the heating ofsaid zone to sever the collapsing wall of said tubulation and to form adome for said bubble.

4. The method of tipping-off a vitreous exhaust tubulation protrudingfrom an evacuated lamp which comprises uniformly heating a zone of theexhaust tubulation to cause the heated wall thereof to collapseinwardly, directing a jet of cooling air at a pressure of about sevenpounds per square inch and of a preselected cross-sectional area at apredetermined area in said heated zone to cause said predetermined areato be driven into said tubulation to join with the opposite wall thereofand to form a bubble thereby closing oif the tubulation and cooling itto prevent undue thinning of the wall of said bubble and continuing theheating of said zone to sever the collapsing wall of said tubulation andto form a dome for said bubble.

5. The method of tipping-off a vitreous exhaust tubulation protrudingfrom an evacuated lamp having a seal which comprises shielding the sealof said lamp from heat, heating uniformly a zone of the exhausttubulation to cause the heated wall thereof to collapse inwardly,directing a jet of cooling air at a pressure of about seven pounds persquare inch and of a preselected cross-sectional area at a predeterminedarea in said heated zone to cause said predetermined area to be driveninto said tubulation to join with the opposite wall thereof and to forma bubble thereby closing ofi the tubulation and cooling it to preventundue thinning of the wall of said bubble and simultaneously stretchingthe collapsing zone of said tubulation longitudinally to thin the wallthereof while continuing the heating of said zone to sever thecollapsing wall of said tubulation and to form a generally sphericaldome for said bubble.

6. The method of tipping-off a vitreous exhaust tubulation protrudingfrom an evacuated device which comprises heating opposite sides of azone of the exhaust tubulation to cause the wall thereof to collapseinwardly, direction a jet of a fluid transverse to the application ofheat and at a predetermined area in said heated zone to cause said areato be driven into said tubulation to join with the opposite wall thereofand to form a bubble thereby closing off the tubulation and cooling itto prevent undue thinning of the wall of said bubble, and continuing theheating of said zone to sever the collapsing wall of said tubulation andto form a dome for said bubble.

References Cited in the file of this patent UNITED STATES PATENTS HowardJuly 12, 1927

